Conventional medical ultrasound imaging systems transmit short bursts of high frequency sound from an array of transducer elements and then receive the sound after it has propagated through tissue and been reflected back towards the transducer array. With knowledge of the speed of sound in tissue, which is typically assumed to be a constant 1540 m/s, an image of the tissue can be created based on the time delay between the transmission and reception of the ultrasound—assuming the sound has traveled directly from the transducer array to the reflecting tissue and directly back to the transducer array. If, however, the sound is reflected multiple times, the time delay will no longer correspond to the physical location of the ultrasound reflector, and structures may appear in the ultrasound image in locations other than their true physical location. These reverberation artifacts can obscure tissue features within the ultrasound image, and can adversely affect the quality of the ultrasound image. The artifacts can be “non-stationary” in that the apparent position of the reverberation artifact is moving relative to the tissue/material being imaged.
Non-stationary reverberation artifacts are likely to occur in, for example, ultrasound therapy devices with separate imaging and therapy transducers coupled to the patient through fluid, where the position of the imaging transducer is fixed relative to the patient and the therapy transducer is moving relative to the patient to vary the focus of the therapy transducer to treat a volume of tissue. In such a system, there may also exist stationary artifacts as a result of multiple reflections of the ultrasound wave off of stationary components within the same device. In such systems, secondary reflections from the therapy transducer or other surfaces are likely to produce artifactual reverberant images within the tissue image, thereby obscuring details of the tissue. Accordingly, there exists a need for removing reverberant artifacts from ultrasound images.